Method and device for pure hydrogen generation from acidic solution

ABSTRACT

The present development is a method for generating pure hydrogen from an organic acid solution and a zero-valent metal. By reacting the metal with the organic acid rather than a mineral acid, hydrogen generation occurs at a gradual and more consistent rate than is observed by prior art methods, making the present method suitable for fuel cell applications. A portable hydrogen-generating device using the method of generating pure hydrogen from acidic solution is further disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent application 60/684,459 filed on May 25, 2005, which is incorporated herein in its entirety by reference.

BACKGROUND

The present development relates to a method and apparatus for generating pure hydrogen from an organic acid solution. The method reacts a pure metal with an organic acid and an oxidizing agent, and generates hydrogen gas having a purity greater than 99.9%. The hydrogen gas is then removed and the metal is precipitated as a metal oxide. In subsequent steps, the metal may be reduced back to zero valency by known methods, such as reaction with a hydrocarbon, and the organic acid is regenerated. Hydrogen generation is gradual and more consistent than observed by prior art methods, making the present method suitable for fuel cell applications.

In recent years, interest has been generated in fuel-cell based engines. These engines have an energy efficiency that is two to three times higher than internal combustion engines (50-55% for fuel cell vs. 15-17% for internal combustion engines). Typically, hydrogen is a supplied directly to a fuel cell to generate electricity.

Hydrogen, however, does not exist in elemental form in nature. Rather, the hydrogen must be liberated from hydrogen-containing compounds. This requires the consumption of energy. For example, water is the most common substance on earth, covering more than 70% of the earth's surface. Water contains about 11% hydrogen by weight, but because of the stability of water, in theory, more than 10,000 joules of energy are needed to obtain one liter of hydrogen gas from water. For commercial operations, hydrogen is commonly derived either from hydrogen-rich chemicals, such as methanol or dimethyl ether, or from fuels, such as coal, natural gas or gasoline. In most cases, liberation of pure hydrogen from the chemicals and fuels is complex and costly.

In order to make fuel cells attractive for application in consumer products, the cost for on-board fuel processing will preferably be less than about $10 per kilowatt. However, using the technology of the prior art, on-board fuel processing costs nearly ten times more than the target. Thus, there is a need for a lower cost alternative. Further, it is highly desirable that for portable appliances fueled by fuel cells, the hydrogen can be generated instantaneously at the moment when the machine is turned on. Due to activation energy requirements for most chemical reaction systems, it is very difficult to overcome the start-up issues by conventional reforming or shift reactions.

SUMMARY OF THE INVENTION

The present development is a method for generating pure hydrogen from an organic acid solution and a portable hydrogen-generating device. A zero-valent metal is reacted with an organic acid and an oxidizing agent. Hydrogen gas generated by the reaction is removed and the metal is precipitated as a metal oxide. In subsequent steps, the metal may be reduced back to zero valency by known methods, such as reaction with a hydrocarbon, and the organic acid is regenerated. Hydrogen generation is gradual and more consistent than observed by prior art methods, making the present method suitable for fuel cell applications. A portable hydrogen-generating device using the method of generating pure hydrogen from acidic solution is further disclosed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graphical representation of hydrogen production over time resulting from the method of the present development—reaction of iron and an organic acid—versus hydrogen production over time resulting from a prior art method—reaction of iron and a mineral acid; and

FIG. 2 is a drawing of a portable hydrogen-generating device made in accordance with the present development.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is a renewable hydrogen generation system. By reacting an organic acid and metal, hydrogen generation can occur at ambient temperature, defined herein as temperatures less than about 35° C., and ambient pressure, or at pressures of about 1 bar. The purity of the hydrogen generated is greater than 99.9%, and the hydrogen can be generated continuously at an essentially steady rate.

As shown in FIG. 1, when approximately one gram of iron powder is reacted with from about 100 mL to about 300 mL acid, hydrogen gas is generated. When the iron powder is reacted with a mineral acid, such as hydrochloric acid, the initial hydrogen generation is extremely rapid and then the production rate holds steady. By contrast, when the iron powder is reacted with an organic acid, such as formic acid or acetic acid, the initial hydrogen production rate is less abrupt with a gradual increase in hydrogen production. In situations where a hydrogen storage tank is not available, it is preferable to have a gradual, consistent rate of hydrogen production. Thus, it is advantageous to have a method for harnessing the hydrogen produced by these organic acid plus metal reactions.

The method of the present invention is intended for use in a portable hydrogen-generating device. The method comprises the steps of:

-   -   (a) reacting a zero-valent metal with an organic acid, and         optionally an oxidizing agent, thereby forming a metal-O—CO—R         complex;     -   (b) removing the hydrogen produced by the reaction of the metal         and acid;     -   (c) regenerating the organic acid by oxidizing the metal-O—CO—R         complex by reacting the complex with an oxidizing agent;     -   (d) precipitating the metal as a metal oxide; and,     -   (e) optionally, reacting the metal oxide with a hydrocarbon to         reduce the metal to the zero-valent state.

The reaction occurs at essentially ambient temperature, defined herein as at a temperature of less than about 35° C. Further, the reaction occurs at essentially ambient pressure or at about 1 bar.

The metal may be any metal that can be easily oxidized in the presence of mild aqueous acid, such as iron, zinc, copper, aluminum, nickel and a combination thereof. The metal may be in the form of powder, granules or pellets and acidic aqueous solution. Iron has been found to be particularly effective for the reaction both in terms of hydrogen yield and with respect to being a relatively low cost metal source.

The organic acids are selected on the basis of a steady hydrogen production rate during a period of time and the absence of additional cations or anions in the solutions. The organic acid may be any RCOOH or HCOOH compound, including carboxylic acids, formic acid, acetic acid, oxalic acid, and combinations thereof.

The oxidizing agent may be any oxidant that can oxidize the M—O—CO—R complex with concomitant formation of the free acid HO—CO—R. Such agents would include, without limitation, hydrogen peroxide, oxygen, ozone, starches and sugars.

The present invention further includes a portable hydrogen-generating device designed around this method. With reference to FIG. 2, the device proposed would include a case (D) housing a first cartridge (A) filled with the metal, a solution recycle column holding additional solution of organic acid (C) and, optionally, the oxidizing agent, and an optional a second replacement cartridge filled with metal (B). The recycle column is plumbed to both cartridges with valves to allow the recycle column to be inline with the cartridge in use. A variable speed pump moves the solution between the active reaction cartridge and the recycle column. When fed to the active reaction cartridge, the organic acid and oxidizing agent solution is preferably fed across the metal as uniformly as possible, such as may be accomplished by using a solution distribution plate or a spray nozzle. The hydrogen gas formed in the active reaction cartridge is vented from the cartridge and case to any desired location. To minimize the risk of contamination of the hydrogen gas by mist or other gases, a hydrogen-permeable membrane is preferably mounted between the metal and the hydrogen vent.

It is noted that although there is significant prior art that teaches hydrogen generation from the reaction of iron with mineral acids, reactions between iron and organic acids are less well-known. Further, the present development includes experimental data showing surprising results—exceptionally high purity and very good yields for hydrogen production at a steady hydrogen production rate—when iron metal is reacted with an organic acid.

It is understood that the processing conditions and apparatus designs may be varied as known to those skilled in the art without exceeding the scope of this development. 

1. The method comprising the steps of: (a) reacting a zero-valent metal with an organic acid, thereby forming a metal-O—CO—R complex; (b) removing the hydrogen produced by the reaction of the metal and acid; (c) regenerating the organic acid by oxidizing the metal-O—CO—R complex by reacting the complex with an oxidizing agent; and, (d) precipitating the metal as a metal oxide.
 2. The method of claim 1 further including the addition of an oxidizing agent with the organic acid.
 3. The method of claim 1 further including the step of reacting the metal oxide with a hydrocarbon to reduce the metal to the zero-valent state after precipitation of the metal oxide.
 4. The method of claim 1 wherein the metal is selected from the group consisting of iron, zinc, copper, aluminum, nickel and a combination thereof.
 5. The method of claim 1 wherein the organic acid is selected from the group consisting of carboxylic acids, formic acid, acetic acid, oxalic acid, and combinations thereof.
 6. The method of claim 1 wherein the oxidizing agent in step (c) is selected from the group consisting of hydrogen peroxide, starches and sugars.
 7. The method of claim 1 wherein the oxidizing agent in step (c) comprises oxygen or ozone.
 8. A portable hydrogen-generating device comprising a case housing (i) a first cartridge filled with a metal and (ii) recycle column filled with an organic acid solution, wherein said recycle column is plumbed to said cartridge, and a variable speed pump connected to the system so as to move said acid solution between the active reaction cartridge and the recycle column.
 9. The device of claim 8 further including a second replacement cartridge filled with metal plumbed to said recycle column.
 10. The device of claim 8 further including at least one valve within the plumbing to allow said recycle column to be in communication with each cartridge separately.
 11. The device of claim 8 wherein said recycle column further includes an oxidizing agent.
 12. The device of claim 8 further including a means for uniformly dispersing said organic acid solution.
 13. The device of claim 8 further including a means for venting gas from said case.
 14. A process for generation of hydrogen gas, comprising the following steps: (a) bringing an organic acid, or solution thereof, into contact with a metal which dissolves in said acid with evolution of hydrogen; (b) reacting the resulting solution containing said dissolved metal with an oxidizing agent; and (c) regenerating said acid by precipitation of said dissolved metal in the form of an oxide.
 15. The process of claim 14 comprising the additional step of passing the evolved hydrogen through a hydrogen-permeable membrane.
 16. The process of claim 14 wherein said metal comprises iron.
 17. The process of claim 14 wherein said oxidizing agent comprises oxygen, ozone, or hydrogen peroxide.
 18. The process of claim 14 wherein said oxidizing agent comprises hydrogen peroxide.
 19. The process of claim 14 wherein said organic acid contains a —COOH group.
 20. The process of claim 14 wherein said organic acid is selected from the group consisting of formic acid, acetic acid, oxalic acid, and combinations thereof. 